7. Circadium Rhythms

• Biological rhythms

  • Distinct patterns of changes in body activity that conform to cyclical time periods
  • Governed by endogenous pacemakers and exogenous zeitgebers
  • Ultraradium rhythms - many times a day, less than 24 hours, hunger/eating cycles
  • Circadium rhythms - 24 hours, sleep/wake cycle, core body temp
  • Infradiam rhythms - longer than a day, more than 24 hours, menstrual cycle
• Sleep/wake cycle

  • Drowsy at night and alert during the day demonstrates the effect of light - exogenous zeitbeger - on our sleep cycle
  • Governed by an endogenous pacemaker called the suprachiasmatic nucleus (SCN)
  • Lies just above the optic chiasm providing info from the eye about light
  • EZ's can reset the SCN
• Siffre's cave study

  • Aim - to investigate his biological rhythms
  • Procedure - spent 2 months in a cave, without natural light or external cues
  • Results - he settled into a natural rhythm just beyond 24 hours (25)
  • Conclusion - we have ‘free running’ biological rhythms, just beyond 24 hrs that are endogenous
• Aschoff and Wever

  • Aim - to investigate biological rhythms
  • Procedure - pps spent 4 weeks in WW2 bunker, without natural light/external cues
  • Results - all but one showed ‘free running’ cycle of 25 hrs (except 1 - 29 hrs)
  • Conclusions - endogenous rhythms - become entrained by exogenous zeitgebers
• Folkard

  • Aim - to investigate biological rhythms
  • Procedure - 12 ps lived in cave for 3 weeks with clocks dictating bed (11.45) and getting up (7.45). The researchers gradually sped up the clock so that a 24 hr day was actually only 22 hrs
  • Results - only 1 pps adjusted to this easily
  • Conclusions - a strong ‘free running’ endogenous clock that is hard to override with exogenous zeitgebers
• AO3 - Strength of supporting research

  • Siffre - results show that ‘free-running’ biological rhythm settled down to one that was beyond usual 24 hours (25 hours), concluding that people have ‘free running’ biological rhythms, just beyond 24 hrs that are endogenous
  • Aschoff and Wever - studies suggest the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but entrained by exogenous zeitgebers associated with our 24 hour day (such as number of daylight hours)
  • Folkard - supports existence of strong free-running circadian rhythm that cannot easily be overridden by EZ's
• AO3 - Limitation of issues with research

  • Small sample sizes of 1 and 12 used in studies meaning research is unrepresentative of society and non-generalisable
  • Czeisler et al. found that sleep/wake cycles can vary from 13-65 hours and this large range is due to impacts of individual differences eg. nightly work shifts and insomnia/hypersomnia - hard to generalise theories and studies
  • Similar to Duffy et al. with morning people and night people
  • Research is flawed
• AO3 - Strength of real-world application

  • Boivin et al. - night workers experience reduced concentration around 6 in the morning (circadian trough)meaning accidents are more likely
  • Knutsson - shift workers are 3 times more likely to develop heart disease than people who work more typical shift patterns
  • Research on circadian rhythms allows people like shift workers to take preventative measures such as splitting up night shifts to ensure they receive enough sleep and increase concentration levels
  • Fewer economic implications
  • Real world value